where \(z_x = x - x^\star \) , \(z_y = y - y^\star \)  are the tracking errors; \(\alpha _x\)  (resp. \(\alpha _y\) ) is a constant parameter which is chosen by the practitioner such that \(\dot{x}\)  and \(\alpha _x u\)  (resp. \(\dot{y}\)  and \(\alpha _y v\) ) are of the same order of magnitude; \(F_x\)  and \(F_y\) , which are data-driven, subsume the poorly known structures and disturbances. A real-time estimation ([1]}) of \(F_x\) , \(F_y\)  are given by 
\(F_x^{\rm est} = - \frac{6}{\tau _x^{3}} \int _{t-\tau _x}^t \left( (t-2\sigma )x(\sigma ) + \alpha _x \sigma (\tau _x - \sigma )u_{\rm MFC}(\sigma )\right)d\sigma \) 
